Saturday, May 10, 2014

Height, Flynn Effect, and shared environment

Some interesting examples of shared environmental effects on height.
Atlantic: ... a database of 2,236 British soldiers who served in World War I, and then they looked up their birth records. The soldiers were relatively representative of the male population as a whole—about two-thirds of the 1890 British male birth cohort enlisted. It turns out that subtle differences in their heights hinted at their origins:

Those from white-collar backgrounds were taller: This follows the theory that wealth buys better food and living conditions, and thus greater height in adulthood. The men who hailed from the top two social classes stood a half-inch taller, on average.

The more kids there were in a household, the shorter they were: Not only because there was less food to go around, but also because it made it more likely that there were more people in each bedroom. “Crowding can help spread respiratory and gastrointestinal infections,” Hatton said. “People sneezing on each other, that sort of thing.” Each additional sibling cost the men an eighth of an inch, and having more than one person per bedroom shaved off a quarter-inch.

Children of literate mothers were taller: When mothers couldn’t read, they were less likely to know about the importance of a balanced diet or clean cutlery. The researchers measured the percentage of women by region who were only able to sign their marriage certificates with an X, rather than their name. People from areas with a high percentage of illiterate mothers were a quarter-inch shorter.

People from industrial districts were shorter than those from agricultural areas: Regardless of income, the Dickensian living conditions of 19th century British cities suppressed height by about nine-tenths of an inch.
Average European male height increased 11 centimeters between 1870 and 1970, about a centimeter per decade, or 1.5 SD in a century. Seems suspiciously similar to the Flynn Effect! In addition, over the same period of time average years of schooling went up significantly: e.g., UK 1870 4 years to 1930 7 years (see Appendix A of this paper). Most individuals born 100 years ago experienced significant deprivation by modern standards.

My own view is that there is nothing particularly mysterious about the Flynn Effect: living conditions, nutrition, and availability of education have all improved drastically in the last 150 years. So g scores should have as well. The Flynn Effect can be consistent with high heritability for non-deprived individuals in modern environments.

See also Swedish height in the 20th century and Flynn on the Flynn Effect.

The north-south gradient in average height found in Europe (see figure) may be a consequence of differential selection pressures that vary by region.


James D Miller said...

Do you think that differences in "living conditions, nutrition, and availability of education" play a major role in explaining differences in IQ among present day Americans?

steve hsu said...

Within the range of environments found in twin and adoption studies, No.

Outside this range? Possibly. See Turkheimer's work (various posts on this blog) on decreased heritability due to deprivation.

JayMan said...

It's worth mentioning that changes in average height weren't monotonic in the U.S., at least. Peter Turchin found that average height declined through the late 19th century only to rise again in the 20th century:

Inequality of Wealth. Inequality of Health. | Social Evolution Forum

JayMan said...

For the record, the attenuation of heritability by SES doesn't always show up. Many (quite large) studies have failed to find such.

Status (SES) and Children's Intelligence (IQ): In a UK-Representative
Sample SES Moderates the Environmental, Not Genetic, Effect on IQ

steve hsu said...

Hence "Possibly" :-)

Mark said...

Does this really mean that the average person in the history books was relatively stupid by modern standards? (Except a lucky few with good nutrition and sanitation?) It seems if that were true you should see its effects written all over history, e.g. maybe changes correlate with things like start of Renaissance or Industrial Revolution. Is there any evidence that is true? Or is it the case that the average intelligence is basically irrelevan for some reason? Eg.. most histotical actors are upper class so less subject to effect, or Flynn effect moves average more than maximum?

chinerpeoprestink said...

dis is no true.

steve confuse.

mzt-dzt studies meaningless.

mza study find significant difference between mza and mzt.

chinerpeoprestink said...

ye. goo. now when frynn effec effec chiner wash ou! we wirr arr be rearry smar.

too ba no drynn effec for peni si.

5371 said...

You lost me with "Peter Turchin found".

nooffensebut said...

For the SAT, much has been made of the larger racial gap at low income levels. The gap is actually maximized at low incomes and high levels of parents' education.

stevesailer said...

The Dutch growing so tall was a surprise -- I don't recall anybody mentioning when I was young in the 1960s and 1970s that the Dutch were particularly tall.

stevesailer said...

One interesting thing I saw in a study of South Korean boys was that youngest generation was spectacularly taller than the previous generation at about age 11 or 12 -- like half a foot taller -- but then the gap between the generation shrank by age 17 to several inches, which is still a lot, but quite a bit less than before puberty. I'm guessing that if you grow up in an environment where famine is a possibility, your body may not want to commit early to how tall you'll wind up since you can't get shorter if food turns out to be in short supply.

steve hsu said...

They were not historically tall.

steve hsu said...

Yes, it seems to me that in environments where food availability is unpredictable one successful adaptation would be to be on the small side, or to have the flexibility to develop in reaction to the availability of calories. If you believe at all in epigenetics you might guess that it could take several generations of good nutrition for a population to reach its full size potential. The information about food availability would be useful to pass on inter-generationally.

Christy2012 said...

Many of these data sets splice together conscription records and other data, so I would be reluctant to read too much into the trends trends of any one country or compare country to county.

Some observations:

1: The dutch exclude most of their immigrants from these more recent data sets (3rd generation only).

2: The data suggests they stopped growing around 1997 [see fig 2]

3: Many other european countries stopped or slowed their growth -- including many of the welfare states (e.g. Finland, Norway, etc).

4: The dutch may not have always been the tallest, but the northern european as a group (especially Norway and Sweden) were clearly taller between 1850 and the 1980s cohorts in the available data and these broad regional trends have not changed that much (some convergence from italy and the like, but they've also leveled off).

5: Contrary to the atlantic article, non-hispanic white & black males actually grew a bit

6: For what it's worth, completely anecdotally, it seems to me that most Americans of similar heritage are also very tall (including my myself & family), so I am especially skeptical of these claims that there is something in the water there or what have you would explain most or all of these international differences :P

Lemongrab said...

If, as you say, epigenetic effects for non-adequate nutrition exist then these might serve as a good candidate for all the Flynn effects. It does seem like the Flynn effect is a multi-generational response to the removal of negative conditions and it would be helpful as it doesn't seem like there is a linear response to malnutrition for IQ, unless it is extreme.

dxie48 said...

Just saw this.

"Shorter Men Live Longer: Association of Height with Longevity and FOXO3 Genotype in American Men of Japanese Ancestry" said...

The Flynn Effect is very mysterious:

1) Does it reflect a genuine rise in intelligence or just greater trust sophistication caused by more education and media?

2) Does it reflect an increase in g or the non-g component of intelligence?

3) is it caused by nutrition or schooling or both?

4)If it's caused by schooling, why does it show up on culture reduced IQ tests?

5)Does it affect the entire distribution or primarily the lower end, and if it's the former, why were theta so many "Geniuses" in the past, despite the small population?

Blog Archive